Feeling the swelling in her crotch Tiff pulled down her pants to reveal a growing bulge in her panties. She took those off too to free her growing erection. Her cock wasn't as big as Katie's yet, but it was still increasing in size. Overcome with intense sexual urges, just as Katie had been before her, she began to masturbate uncontrollably. The sight of the gorgeous, hairy man that her friend had become only furthered her arousal. More than anything in the world she wanted to be like that, covered in muscle and hair with a glorious cock between her legs.
"Oh god Katie! It feels so good, help me!" Tiff fell to her knees, unable to remain standing due to the forces running through her body.
Katie didn't want to admit it, but the sight of Tiff's growing cock was starting to turn him on. He didn't want to fuck another girl, but he'd never seen a girl with something like that between her legs.
Moaning in bliss Tiff began to rub at her breasts, enjoying them while they lasted, "Please Katie, suck my dick!"
Such a request should have disgusted him, but now Katie found himself curious as to what it would be like to try the taste of his friend's cock. Would it be salty with sweat and would the flavor change as new hormones flooded through her body? Unable to resist any longer he helped Tiff to her feet and knelt with his face to her crotch. For a moment he savored the musky scent of her pussy, which wouldn't be there for long, then he took her throbbing cock into his mouth, amazed at how much of it he could fit in without gagging. Tiff wove her fingers through his hair, pressing his face against her as she thrust savagely into his mouth. Her strokes grew shorter and swifter as her breath came in sharp little gasps. He could taste something salty beginning to seep into his mouth, then Tiff tensed and it was like an explosion going off in his throat.
Choking he pulled away, dribbles of cum running from the sides of his mouth and a long strand of saliva trailing from his lips to Tiff's now soft cock. In addition to her cock, Tiff now had a pair of balls dangling down and sending testosterone pumping into her bloodstream.
Katie spat onto the floor and looked up at Tiff, "Not bad for a first time?"
For her reply Tiff knelt down and kissed him, but he pulled away, since at the moment it was too much like kissing a girl.
She laughed, a few fine hairs already beginning to sprout on her face, "Am I still too much of a girl for you?"
"Not for much longer," Katie laughed, marveling at the sound of his new deeper voice. It was impossible to believe that just minutes ago he was shocked by the sound of it.
The hairs on Tiff's face had thickened into a full fledged beard and she took off her shirt just in time to reveal her breasts shrinking, soft pads of fat giving way to wonderful, firm muscle. Seeing hair sprout over Tiff's new muscular frame, like grass growing in a time lapse video was too much for Katie and he found himself getting hard again.
Tiff noticed this right away, "Can I return the favor you just gave me?"
Her voice was a deep masculine rumble, too sexy to resist. He allowed Tiff to take his cock in her mouth and suck on him. It felt so good that he was at a loss to find any experience he'd had as a girl to compare it to. Tiff's tongue teasing the length of his cock while her lips caressed its base was the most wonderful thing he'd known, even better than watching her become a man and pleasuring her until she came in his mouth. All too soon he felt a sort of indescribable churning, emanating either from the pit of his stomach, or maybe his balls, and he shot cum down Tiff's throat.
She managed better than he had, swallowing every last drop and licking her lips afterward, "Delicious."
"What now?" Katie wondered as he looked at the handsome young man his best friend had become.